Digimon Cyber Sleuth: Best way to get stats up?

You need to train the stats on your DigiFarm. Are you able to get hold of the items that can change a Digimon's personality? (The online plaza store I think, not sure which chapter they unlock in) Taking WereGarurumon as an example, you'd change the Farm's leader to Defender and the WereGarurumon to Defender too. He'll start earning additional stat points in DEF.

(Basically two things determine which stat gets the increase - the personality of the leader and the personality of the digimon being trained)

All digimon can earn 50 extra stat points from training, so if you leave him on the DigiFarm until he earns all 50, then that's perhaps at least 30 less levels you need to get him to before he can evolve to MetalGarurumon. Also just by being Defender, his DEF is boosted by 5%.

What you're talking about with the evolving and regressing, is the ABI stat, which raises when you do those. As above, Digimon can earn 50 extra stat points normally, and 1 more for each 2 ABI, so another 50 max, for a total of 100. Without doing the training, a Digmon with 0 ABI has the same stats as one of the same level/personality with 100 ABI, but the one with 100 can earn more points by training, it has more potential.